[44.11] A Dynamical Study of the Low Mass X-ray Binary GX 349+2

S. Wachter (U. of Washington)

We have obtained simultaneous optical photometry and spectroscopy of the
low mass X-ray binary (and Z-source) GX 349+2 with the CTIO 0.9 m and
4 m telescopes in
July 1997. The spectrum of GX 349+2 only shows strong, narrow H\alpha emission.
The observed radial velocities indicate that our previously reported
22 hour photometric modulation is indeed the orbital period. We find
\gamma=-250\pm10 km s^-1 and K=65\pm6 km s^-1 for the systemic
and semi-amplitude velocities respectively. The photometric
light curve and radial velocity curve are offset by 0.25 in phase.
Doppler tomography shows the H\alpha emission centered on the position
of the neutron star.
The relative phasing implies that the photometric variability is probably
caused by the heated face of the companion star while the H\alpha emission
may arise in an accretion disk and traces the motion of the neutron star. It
also indicates
that the emission region is symmetric around the neutron star.
If the H\alpha emission
does originate in the accretion disk, the narrowness of the line suggests a low
inclination for the system.